Evaluation of the wood quality by soft X-ray of crack formation in wood as a result of nailing.

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The mechanical properties of nailed joints are very important for the rational design of timber structures. Above all, crack size induced by nailing is important factor for the strength of nailed joints. There are two objects in this study ; one is to investigate the crack propagation caused by nailing and the other is to evaluate the various kinds of wood quality by a new method.Crack propagation caused by driving a nail has been studied but most of the studies discussed only surface crack characteristics. Some papers have examined the profile of cracks in wood. However, cutting wood after nailing to measure the crack length is a time-consuming method. Staining the crack cavities looks like a promising method, but the stain does not penetrate into a small crack thoroughly. In this study, new methods are proposed. Crack formation in wood induced by nailing was investigated by barium permeation method.The following conclusions were obtained.1) The barium permeation method is effective to measure the crack formation.2) There were three types of cracks ; test tube shapes, oval shapes and corn shapes.3) The effect of nailing methods, the shape of the nail shank, and the shape of nail points have a great influence on the crack length.4) Within a species, there is a high degree of correlation between crack size and wood density, and between crack size and the diameter of nails. It can be expressed as L=krhod^2 where L is a crack length, rho is the wood density, and k is a constant.5)Hinoki generates less crack when nailing and has high withdrawal strength.6)Juvenile wood was cracked less than mature wood.7)Crack formation is related to wood species and quality. The Barium permeation method is an effective measure to evaluate the quality of the domestic soft wood.